It is desirable for tires to have, for example, good wet skid resistance, low rolling resistance, tear strength, and good wear characteristics. In order to reduce the rolling resistance and to improve the treadwear characteristics of tires, rubbers having a high rebound have traditionally been utilized in making tire tread rubber compounds. On the other hand, in order to increase the wet skid resistance of a tire, rubbers that undergo a large energy loss have generally been utilized in the tread of the tire. In order to balance these two viscoelastically inconsistent properties, mixtures of various types of synthetic and/or natural rubber are normally utilized in tire treads. For instance, various mixtures of styrene-butadiene rubber (SBR) and polybutadiene rubber are commonly used as a rubbery material for automobile tire treads. To alter or manipulate the properties of these rubbery polymers, and thus the characteristics of the tire utilizing such rubbery polymer, various compounds may be added to the terminal ends thereof.
Such end functionalized rubber polymers may define block polymers, which are comprised of blocks of different polymerized monomers. These block polymers can be synthesized using anionic addition polymerization reactions. In anionic addition polymerizations, olefinic monomers, for example, may be polymerized after initiation by a strong anionic base, such as an organolithium compound. When the organolithium compound is contacted with a molecule having a terminal C═C bond, a conjugate addition occurs between the carbanion of the organolithium compound and the terminal C═C bond. This conjugate addition forms a new carbanion centered on the monomeric moiety, which subsequently reacts with additional olefinic monomer to form a living polymerization reaction. Accordingly, the desired functional monomers may be added to the end of the living polymer.
These end functionalized rubbery block polymers may be utilized in rubber compounds, such as for tire treads. However, rubber compounds, which often include carbon black and/or silica filler, for example, must include the appropriate mix of ingredients so as to provide the resulting tire with desirable characteristics. Unfortunately, due to the unpredictable interactions of the various compounds and chemicals used for compounding these rubbery polymers, it can be challenging to formulate useful rubber compounds that provide tires with overall desirable performance characteristics.
Thus, it would be desirable to provide a rubber compound, such as for use in tire treads, that contains an end functionalized rubbery block polymer, which is hydroxy terminated, wherein such rubbery compound interacts with polar filler and can provide desirable wear properties without substantially sacrificing other performance characteristic(s), e.g., traction properties.